Rock breaking

ABSTRACT

A rock-breaking cartridge (10) includes a casing (16) of deformable material that forms an internal cavity (22) and a tapered part (82). A seal (90) extends around the outside of the tapered part (82) and a piston (92) inside the cavity (22) butts against the inside of the tapered part (82) to seal against the inside of the casing (16). A charge (46) is provided inside the cavity (22) on the side of the piston (92) that is opposite from a narrow end of the tapered part (82) and when the charge (46) is ignited, it causes the piston (92) to slide towards the narrow end and to force the tapered part (82) and seal (90) to expand. The expansion causes the seal (90) to seal against the inside of a hole in which the cartridge (10) has been placed and the seal (90), tapered part (82) and piston (92) form a sturdy plug to contain gasses generated by detonation of the charge (46).

FIELD OF THE INVENTION

This invention relates to rock breaking and more particularly, topyrotechnic devices for fragmenting rocks.

BACKGROUND TO THE INVENTION

Rock breaking is typically employed to break rock in mining, demolition,excavation, and the like and conventional techniques require a hole tobe drilled in rock, a charge to be inserted in the hole, the hole to beclosed behind the charge and the charge to be ignited so that the chargedetonates and the detonation produces sufficient gas pressure tofragment the rock. In order for the charge to perform optimally, thecharge and the pressurised gas must be completely contained against thewall and loss of gas pressure, e.g. along the hole, should be prevented.

Various rock breaking cartridge devices have been developed that can beinserted into such a hole and can be detonated without closing thehole—thus making the process substantially quicker and easier. Some ofthese rock breaking cartridges comprise a casing in the form of aplastic tube that houses the charge and that is closed with plugs atboth ends. These rock breaking cartridges are prone to failure wheninternal components breach the cartridge at opposing ends when underhigh pressure, so that the plugs are blown off at both ends of thecasing—which is not safe and results in poor rock fragmentation (ifany).

The present invention seeks to provide a device for fragmenting rock,which is cost-effective, safe, reliable and easy to use.

SUMMARY OF THE INVENTION

According to the present invention there is provided a rock breakingcartridge comprising:

-   -   a casing of deformable material, said casing forming an internal        cavity and a tapered part;    -   at least one seal extending, at least in part, around the        outside of the tapered part of the casing;    -   a piston disposed inside the internal cavity, said piston being        dimensioned to but against the inside of the tapered part of the        casing and to seal against the inside of the casing; and    -   a gas generating compound inside the internal cavity on the side        of the piston that is opposite from a narrow end of the tapered        part of the casing.

The tapered part of the casing may be frusto-conical, tapering towardsthe narrow end and at least part of the piston may have a frusto-conicalshape.

The piston may include a rounded head that buts sealingly against theinside of the tapered part of the casing and/or may include a skirt thatseals against the inside of the casing.

The seal may be deformable and the cartridge may include grip formationsthat extends around the outside of the tapered part of the casing andthe grip formations may be integrally formed with the casing.

The rock breaking cartridge may include an end cap that seals an end ofthe casing that is opposite from the tapered part and the cap may beheld on the casing by a retainer that may be configured to release thecap from the casing upon a predetermined pressure being reached insidethe internal cavity.

The casing may have two tapered parts, at opposing ends of the casing,with a seal and a piston disposed proximate each of its ends and withthe gas generating compound inside the internal cavity between the twopistons. The casing may comprise two sub-casings, which each have atapered part and the sub-casings may be joined together in a sealingmanner.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how itmay be put into effect, the invention will now be described by way ofnon-limiting example, with reference to the accompanying drawings inwhich:

FIG. 1 shows a longitudinal cross-sectional view of a first embodimentof a rock breaking cartridge according to the present invention, in aninitial condition;

FIG. 2 shows a longitudinal cross-sectional view of a second embodimentof a rock breaking cartridge according to the present invention, in aninitial condition;

FIG. 3 shows a longitudinal cross-sectional view of a third embodimentof a rock breaking cartridge according to the present invention, in aninitial condition;

FIG. 4 shows an external, three-dimensional view of the cartridge ofFIG. 3;

FIG. 5 shows a three-dimensional view of a longitudinal section of thecartridge of FIG. 3, without charge and detonator/squib;

FIG. 6 shows a three-dimensional view of a piston of the cartridge ofFIG. 3;

FIG. 7 shows a three-dimensional view of a seal of the cartridge of FIG.3;

FIGS. 8A and 8B show three-dimensional views from opposing directions,of an end cap of the cartridge of FIG. 3;

FIG. 9 shows a three-dimensional view of a crimp sleeve of the cartridgeof FIG. 3;

FIG. 10 shows a three-dimensional view of a longitudinal section of afourth embodiment of a rock breaking cartridge according to the presentinvention, in an initial condition;

FIG. 11 shows a three-dimensional view of an end-cap of the cartridge ofFIG. 10;

FIG. 12 shows a three-dimensional view of the cartridge of FIG. 3,fitted with an accessory; and

FIGS. 13A and 13B show three-dimensional views from opposing directions,of the accessory of FIG. 12.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a first embodiment of a rock breaking cartridge (or“cartridge”, for brevity) according to the present invention, isgenerally identified by reference number 10 and it has a front end 12and a rear end 14.

The cartridge 10 has a casing or vial 16 of a stiff, but deformablematerial, preferably a durable polymer. The casing 16 forms a closed end18 at the rear end 14 of the cartridge 10 and a tube 20 extending fromthe closed end to the front end 12. The tube 20 is preferablycylindrical, but it can also have other shapes. An internal cavity 22 isdefined inside the casing 16.

Near the rear end 14, there is a seal 24 on the outside of the tube 20.The seal 24 is made from a durable, but deformable material such as apolymer and it is in the form of a ring that extends around thecircumference of the tube 20, spaced from the end 18. On its inside, theseal 24 defines a frusto-conical ramp surface 26 that tapers (narrows)towards the closed end 18, to a point where it forms an apex 28, fromwhere it widens towards the closed end. The seal 24 butts tightlyagainst the outside of the tube 20, so that the tube is retained insidethe seal 24 against expansion, with the walls of the tube following theinside of the seal 24 along the ramp surface 26 and forming a throat 34inside the apex 28.

In other embodiments of the invention, the seal 24 can take many forms,as long as it retains the tube 20 to form a throat, but the seal 24should preferably have one or more ramp surfaces that are preferablyspaced around its circumference.

On the outside of the seal 24 there are a number of grip formations orprotuberances in the form of circumferential ridges 30 that can sealagainst the inner walls of a drilled hole, as well as protuberances 32that give the seal an effective overall diameter that is larger than thedrilled hole size for which it is intended, to grip the inner walls ofthe hole and hold the cartridge 10 in place.

Inside the cavity 22 is a ram or piston 36 that has a taper surface inthe form a frusto-conical outer surface 38 that tapers towards theclosed end 18 and that buts against the inside of the tube 20. Thefrusto-conical shape of the outer surface 38 gives the piston 36 a widerpart 42 at the end of the outer surface closest to the front end 12,with a diameter that is more than the diameter of the throat 34, and anarrow part or narrow end 40 at the side of the outer surface that isclosest to the closed end 18, with a diameter that is less than thediameter of the throat. The piston 36 is positioned in the tube 20 withits narrow end 40 adjacent the throat 34 and with its wide part 42farther to the front end 12.

The outer surface 38 seals against the inside of the tube 20, but canslide longitudinally along the tube and its seal against the tube isenhanced, especially under high pressure, by a seal element such as anO-ring 44.

In other embodiments, the piston need not be frusto-conically shaped,but could have one or more ramped surfaces that taper from a wider partto a narrower part.

A gas generating compound or charge 46 fills the cavity 22 between thepiston 36 and the front end 12 and a charge initiator or squib 48 isembedded in the charge. Electric wires 50 extend from the outside of thecartridge 10 to the squib 48 and are routed through apertures in thepiston 36 and closed end 18, with a sealing compound 52 sealing againsthigh pressure and water around the wires as they pass through the pistonand with a gland 54 sealing against water around the wires as they passthrough the closed end. The gland 54 is disposed eccentrically in theclosed end 18 so that the wires 50 are routed eccentrically from therear end 14 of the cartridge 10—which reduces the risk of damaging thewires 50 as the cartridge is inserted into a hole.

At the front end 12, the tube 20 is closed with an end cap 56 that isheld in place by a retaining ring 58 that extends around the outside ofthe tube and compresses the tube inwardly into a circumferential groove60 on the cap. The retaining ring 58 and groove 60 are configured sothat the cap 56 is only held on the end of the tube 20 until apredetermined pressure is reached inside the cavity 22. The outercircumference of the cap 56 seals tightly against the inside of the tube20 and its seal is enhanced, to ensure water tightness, bycircumferential sealing grooves, filled with a sealing compound 62. Theend of the cap 56 that extends towards the cavity 22 is hollow, with thecharge extending into the cap, so that expanding gasses from the chargecan expand the walls of the cap to seal against the inside of the tube20.

In use, when matter such as rock needs to be fragmented, a hole isdrilled in the rock and the cartridge 10 is inserted in the hole withits front end 12 first, to a desired position, with the wires 50extending from the rear of the cartridge out of the hole. The cartridge10 is intended for use in a blind hole, with the front end 12 againstthe blind end of the hole. When in position, the protuberances 32 holdthe cartridge 10 in place, irrespective of the orientation of the hole,and ensure that the cartridge is supported generally concentricallyinside the hole. Up to this point, the cartridge 10 is still in itsinitial condition, as described above, with reference to FIG. 1.

Once the cartridge 10 is in position, the charge 46 is ignited with thesquib 48 and detonates to expand rapidly. During the initial expansion,the end cap 56 is retained on the tube 20 and increasing pressure in thecavity 22 pushes the piston 36 towards the closed end 18. The piston 36slides longitudinally along the tube 20 towards the closed end 18 andwhile doing so, the frusto-conical outer surface 38 presses against thetube 20 and the seal 24 and causes the tube and seal to expand. Theexpansion of the seal 24 causes it to press firmly against the insidewalls of the hole and as the piston 36 progresses inside the seal,pressure in the cavity from the expanding charge further presses theseal against the walls of the hole. At this point, the seal 24 sealsfirmly against the walls of the hole and the seal and piston 36 form avery sturdy plug in the hole.

The charge 46 continues to expand and expands the tube 20 which bulgesand when the pressure gets higher, the retaining ring 58 fails to keepthe tube in place on the end cap 56, so that the end cap and tube areexpanded tightly against the walls and end of the hole, while the piston36 and seal 24 remain in place, or the piston slides slightly furtherinto the seal and enhances its seal and locating function.

Eventually, the expanding charge 46 fragments the rock surrounding thehole with a heaving effect, but up to the point that the rock isfragmented, the plug formed by the piston 36 and the seal 24 containsthe expanding charge in the blind end of the hole.

The invention shown in FIG. 1 holds various advantages, including:

-   -   effective sealing with a casing with only one open end;    -   low cost to manufacture and assemble;    -   only low pressure required to slide the piston 36 to seal the        seal 24 against the hole wall;    -   the size of the charge 46 can be varied by altering the length        of the tube 20, without a need for additional tooling;    -   the cartridge 10 is watertight;    -   the cartridge is self-sealing against the walls of the hole;    -   the position of the squib 48 can be varied to adjust ignition        performance and the rate and timing of the sliding action of the        piston 36, preferably with a delay before the end cap 56 is        blown off the tube 20;    -   the seal 24 has grip formations in the form of the ridges 30 and        protuberances 32 that seal against the inside walls of the hole        and that hold the cartridge 10 in place; and    -   the closed end 18 of the tube 20 prevents the internal        components of the cartridge 10 from breaching the cartridge at        high pressure, thus enhancing safety and blasting performance.

Referring to FIG. 2, a second embodiment of a rock breaking cartridgeaccording to the present invention, is generally identified by referencenumber 70 and features that are common between the first embodiment andthe second embodiment of the invention, are identified by like referencenumbers and duplicates of those features are identified by a suffix“0.1”.

The cartridge 70 also has a front end 12 and a rear end 14 and at itsfront end, it has a casing 16 with a closed end 18, a piston 36 insidethe casing and a seal 24 outside the casing, with a charge 46 inside aninternal cavity 22 and a squib 48 inside the charge that is connected towires 50—all practically identical to the same features in cartridge 10shown in FIG. 1. However, the cartridge 70 does not have an end cap atits front end 12, but instead has another casing 16.1 with a closed end18.1 at the front end 12. A seal 24.1 extends around the casing 16.1near the closed end 18.1 and does not have protuberances 32. Likewise, apiston 36.1 is provided inside the casing 16.1 for interaction with theseal 24.1. The casing 16.1, seal 24.1 and piston 36.1 are almostidentical to the casing 16, seal 24 and piston 36 at the rear end 14,but their orientations are inverted and they do not have provision forwires 50.

The open ends of the tube 20 at the rear of the cartridge 70 and a tube20.1 at the font of the cartridge, face each other and are connectedtogether in a sealing manner by a joining nipple 72 that spans theinsides of the two tubes in the vicinity of their open ends, and aswaging sleeve 74 that extends around the open ends of the two tubes andholds them tightly against the joining nipple, so that the tubes 20 and20.1 effectively form a single tube with two closed ends 18 and 18.1.

The cavity 22 inside the casing 16 can be open to a cavity 22.1 insidethe casing 16.1 and both these cavities are filled with a charge 46, butfor ease of assembly, a thin charge divider 76 is provided between thetwo charges, to hold the charge 46 in place inside the rear tube 18,while it is being attached to the front tube 18.1.

In use, the cartridge 70 is also inserted into a hole in rock that needsto be fragmented, similar to the cartridge 10, but the hole is not ablind hole or the cartridge is not installed at the end of the hole, butis installed at a desired position with the hole extending from bothends 12,14. Up to this point, the cartridge 70 is still in its initialcondition, as described above, with reference to FIG. 2 and with thewires 50 extending from the rear end 14 out of the hole and with theprotuberances 32 holding the cartridge in place.

Once the cartridge 70 is in position, the charge 46 is ignited with thesquib 48 and detonates to expand rapidly. The ignited charge 46 burnsthrough the charge divider 76 and/or ruptures the charge divider, sothat the charge 46.1 is also ignited. During the initial expansion, theincreasing pressure in the cavities 22 and 22.1 pushes the pistons 36and 36.1 outwards, towards their respective closed ends 18 and 18.1 andthe pistons slide inside tubes 20 and 20.1 and expand the seals 24 and24.1 as described above with reference to FIG. 1, so that the seals sealfirmly against the walls of the hole and the seals and pistons form verysturdy plugs on opposing sides of the charges 22 and 22.1.

The charges continue to expand and expand the tubes 20 and 20.1 whichbulge and are expanded tightly against the walls of the hole, while thepistons 36 and 36.1 and the seals 24 and 24.1 remain in place, or thepistons slide slightly further into the seals and enhance their sealsand locating functions.

Eventually, the expanding charge fragments the rock surrounding the holewith a heaving effect, but up to the point that the rock is fragmented,the plugs formed by the pistons 36 and 36.1 and the seals 24 and 24.1contain the expanding charge in the hole.

The invention shown in FIG. 2 holds the same advantages mentioned above,in relation to FIG. 1, as well as further advantages following from itscasing having two closed ends 18 and 18.1, including:

-   -   effective sealing of the cartridge 70;    -   the cartridge is self-sealing against the walls of the hole and        at both ends; and    -   the closed ends 18 and 18.1 of the tube 20 prevent the internal        components of the cartridge 70 from breaching the cartridge at        high pressure, thus enhancing safety and blasting performance.

Referring to FIGS. 3 to 9, a third embodiment of a rock breakingcartridge according to the present invention, is generally identified byreference number 80 and features that are common between the firstembodiment and the third embodiment of the invention, are identified bylike reference numbers.

The cartridge 80 has a front end 12 and a rear end 14 and includes acasing 16 of a stiff, but deformable material such as a durable polymerthat is preferably injection moulded. The casing 16 forms a cylindricaltube 20 for most of its length and a tapered part 82 along about therear third of the length of the cartridge 80. The tapered part 82 tapersfrusto-conically towards the rear end 14, where it is closed off with agrommet 84. The casing 16 also includes a number of radial ribs 86 thatextend from the outside of the wider end of the tapered part 82, toreinforce the tapered part 82, but this reinforcement is only providedon the wider end of the tapered parte (i.e. only on the pressure side ofthe piston head 96—see below). Two of the ribs 86 protrude outwardlywith a diameter that is more than the rest of the cartridge 80 and serveas retaining elements, like the protuberances 32 in FIGS. 1 and 2, forretaining the cartridge 80 in place in a hole. In a preferredembodiment, the two protruding ribs can be replaced with retainingelements in the forms of protruding fingers.

At the rear end 14, the casing 16 forms a hollow, ribbed collar 88 thatreinforces the casing around the grommet 84.

A sealing/plugging element in the form of a seal 90 of durable, butdeformable material such as a polymer (e.g. plasticised PVC rubber),forms a ring around the tapered part 82 between the ribs 86 and theshoulder 88. The seal 90 includes a number of grip formations orprotuberances in the form of circumferential ridges 30 on its outersurface. On its inside, it has a tapered shape that buts against theoutside of the tapered part 82.

An internal cavity 22 is defined inside the casing 16 and a ram orpiston 92 of a hard, durable polymer, or the like, is fitted inside thecavity in the vicinity of the ribs 86. The piston 92 is hollow and has agenerally tapered (frusto-conical) shape that is wider and open at itsfront and tapers to a closed rear end 94, so that the inside of thepiston is contiguous with the cavity 22, although reinforcing webs 95are provided in the hollow inside of the piston.

At its rear end 94, the piston 92 forms a rounded head 96 that butstightly against the inside of the tapered part 82 inside the front ofthe seal 90. At the front of the piston 92, it forms a circumferentialskirt 98 at its widest point and the skirt seals tightly against theinside of the tube 20 to the front of the tapered part 82. The taperedpart 100 of the piston 92, between the head 96 and skirt 98, is recessedso that it is spaced slightly inwardly from the inside of the taperedpart 82 of the casing 16.

At the front end 12, the tube 20 is closed with an end cap 102 that isheld in place by a crimp sleeve 104 that extends around the outside ofthe tube and compresses the tube inwardly into a circumferential recess106 on the cap. The rear of the cap 102 is hollow and defines agenerally cylindrical skirt 108 that seals tightly against the inside ofthe tube 20, with internal webs 110 reinforcing the skirt.

The end cap 102 defines a central passage 112 extending longitudinallyfrom the front 12 of the cartridge 80 to the internal cavity 22 and thepassage is closed off by a threaded plug 114. At the front of the endcap 102, a nose cone 116 is formed by radial webs 118 extending aroundthe passage 112, each web with a rounded, tapered profile.

A charge 46 fills the cavity 22 between the piston head 96 and end cap102 (including the hollow insides of the piston 92 and the skirt 108)and a squib 48 is embedded in the charge. Electric wires 50 extend fromthe outside of the cartridge 80 to the squib 48 and are routed throughan eccentric aperture in the collar 88 and central apertures in thepiston 92, in a sealing manner.

In use, when matter such as rock needs to be fragmented, a hole isdrilled in the rock and the cartridge 80 is inserted in the hole withits front end 12 first, to a desired position, with the wires 50extending from the rear of the cartridge out of the hole.

The cartridge 80 is intended for use in a blind hole, with the front end12 against the blind end of the hole. When in position, the protrudingribs 86 hold the cartridge 80 in place, irrespective of the orientationof the hole, and ensure that the cartridge is supported generallyconcentrically inside the hole. Up to this point, the cartridge 80 isstill in its initial condition, as described above, with reference toFIGS. 3 to 9.

Once the cartridge 80 is in position, the charge 46 is ignited with thesquib 48 and detonates to expand rapidly. During the initial expansion,the end cap 102 is retained on the tube 20 and increasing pressure inthe cavity 22 pushes the piston 92 towards the rear end 14. The piston92 slides longitudinally rearward inside the casing 16 and initially,the skirt 98 of the piston slides along a short cylindrical part of thetube 20, while the piston head 96 slides rearwards inside the taperedpart 82 and urges the tapered part outwards and causes the seal 90 toexpand. As the piston 92 slides further rearwards inside the casing 16,its skirt 98 slides along the inside of the tapered part 82 in theregion of the ribs. The expansion of the tapered part 82 and seal 90cause them to press firmly against the inside walls of the hole and forma very sturdy plug in the hole.

The charge 46 continues to expand and expands the tube 20, which bulgesand when the pressure gets higher, the crimp sleeve 104 fails to keepthe tube in place on the end cap 102, so that the end cap and tube areexpanded tightly against the walls and end of the hole, while the piston92 and seal 90 remain in place (or the piston slides slightly furtherrearwards and enhances the seal and locating functions of the seal).

Eventually, the expanding charge 46 fragments the rock surrounding thehole with a heaving effect, but up to the point that the rock isfragmented, the plug formed by the piston 92 seal 90, contains theexpanding charge in the blind end of the hole.

The invention shown in FIGS. 3 to 9 holds the same advantages mentionedabove, in relation to FIG. 1, as well as further advantages, including:

-   -   The provision of a passage 112 and plug 114 in the end cap 102        allows the cartridge 80 to be assembled completely in a        manufacturing facility, apart from filling it with its charge        46. The uncharged cartridges 80 can be safely and easily        transported worldwide, to be filled with the charge 46 and have        plugs 114 fitted, at a charge-filling plant.    -   The tapered nose cone 116 makes it easier to insert the        cartridge 80 into a hole where the hole is at a        distance—especially in overhead installations where cartridges        may need to be inserted with long extension poles. The design of        the nose cone 116 with webs 118, prevent stones from wedging the        cartridge, which could have prevented it from being inserted in        the hole.    -   The casing 16 can conveniently be injection moulded—which        improves the accuracy of its wall thickness and the tapered        shape and cone angle of the tapered part 82.    -   The casing 16 is reinforced and restricted in the vicinity of        the rear end 14, to prevent the piston 92 from breaching the        casing when maximum pressure is reached in the cavity 22. The        tapered part 100 of the piston 92 between the skirt 98 and head        96 is reinforced with the webs 95 to limit the stroke of the        piston. When the tapered part 100 of the piston 92 is forced        against the tapered part 82 of the casing 16 at maximum        pressure, the piston retains its structural integrity and is not        extruded through the rear of the casing.    -   The seal 90 is held captive on the tapered part 82 of the casing        16, between the ribs 86, and the collar 88—which effectively        form radial flanges on opposing sides of the seal.    -   The wall thickness of the tapered part 82 of the casing 16 can        be less than the wall thickness of the tube 20. This means that        less force will be required to bulge the tapered part 82        outwards and activate the seal in the hole, and a higher        pressure can build up in the cavity 22, before the tube 20        ruptures.

Referring to FIGS. 10 and 11, a fourth embodiment of a rock breakingcartridge according to the present invention, is generally identified byreference number 120 and features that are common between the thirdembodiment and the fourth embodiment of the invention, are identified bylike reference numbers and duplicates of such features are identified bya suffix “0.1”.

The cartridge 120 also has a front end 12 and a rear end 14 and at itsfront end, it includes an entire cartridge 80 that is identical to thecartridge shown in FIG. 3, except that, instead of an end cap, is has aninternal barrel nipple 124 that defines a large internal passage 112,without a plug. A second cartridge 80.1 is identical to the firstcartridge (apart from not having wires and a squib—which are not shownin FIG. 10), but has an inverted orientation and is also attached to thebarrel nipple 124 instead of having an end caps, so that the passage 112is common between the two cartridges and connects the internal cavities22 and 22.1 of the two cartridges 80 and 80.1.

In use, the cartridge 120 is also inserted into a hole in rock thatneeds to be fragmented, similar to the cartridge 80, but the hole is nota blind hole or the cartridge is not installed at the end of the hole,but is installed at a desired position with the hole extending from bothends 12,14. Up to this point, the cartridge 120 is still in its initialcondition, as described above, with reference to FIGS. 10 and 11.

Once the cartridge 120 is in position, the charge is ignited anddetonates to expand rapidly, causing the pistons 92 and 92.1 to slidelongitudinally in the casings 16 and 16.1 in opposite directions, eachsliding as described above with reference to FIGS. 3 to 9, so that theribs 86 and 86.1 and seals 90 and 90.1 expand and press firmly againstthe inside of the hole to form very sturdy plugs in the hole on bothends of the cartridge 120. The charge continues to expand and expandsthe tubes 20 and 20.1 which bulge and are expanded tightly against thewalls of the hole, until, the expanding charge fragments the rocksurrounding the hole with a heaving effect.

The invention shown in FIGS. 10 and 11 holds the same advantagesmentioned above, in relation to FIGS. 3 to 9, as well as furtheradvantages resulting from the coupling of two cartridges 80 and 80.1,including:

-   -   Increased heaving effect because of the larger charge 46; and    -   Self-sealing of the cartridge 120 against the walls of the hole        and at both ends 12,14.

Referring to FIGS. 12 and 13, the cartridge 80 is shown with a tool oraccessory 128 fitted on the collar 88. The accessory 128 has threefingers 130 that can be inserted into recesses 132 in the rear of thecollar 88 and the accessory defines a central, female threaded aperture134.

The end of an extension pole can be screwed into the aperture 134 sothat the cartridge 80 is held in place on the end of the extension poleby the releasable attachment of the fingers 130 in the recesses 132. Theextension pole can be used to insert the cartridge 80 in hard to reachplaces, such as overhead locations. Once the cartridge 80 has beenplaced, the fingers 130 are easily withdrawn from the recesses 132 andthe extension pole is withdrawn from the cartridge with the accessory128 position on the extension pole.

1. A rock breaking cartridge comprising: a casing of deformablematerial, said casing having a front end and a rear end, said casingforming an internal cavity and forming a tapered part in the vicinity ofthe rear end, with a narrow end of the tapered part being closer to therear end than a wider end of the tapered part; at least one deformableseal extending, at least in part, around the outside of the tapered partof the casing; a piston disposed inside the internal cavity, said pistonbeing dimensioned to but against the inside of the tapered part of thecasing and to seal against the inside of the casing; an end cap disposedat the front end of the casing and sealing the sealing the front end ofthe casing; and a gas generating compound inside the internal cavitybetween the piston and the end cap.
 2. The rock breaking cartridgeaccording to claim 1, wherein the tapered part of the casing isfrusto-conical and tapers towards the narrow end.
 3. The rock breakingcartridge according to claim 1, wherein at least part of the piston hasa frusto-conical shape.
 4. The rock breaking cartridge according toclaim 1, wherein the piston includes a rounded head that buts sealinglyagainst the inside of the tapered part of the casing, inside the seal.5. The rock breaking cartridge according to claim 4, wherein the pistonincludes a skirt that seals against the inside of the casing and thepiston is at least partly hollow and defines an inside that iscontiguous with the part of the cavity in which the gas generatingcompound is disposed.
 6. (canceled)
 7. The rock breaking cartridgeaccording to claim 1, which includes grip formations that extend aroundthe outside of the tapered part of the casing.
 8. The rock breakingcartridge according to claim 7, wherein the grip formations areintegrally formed with the casing.
 9. The rock breaking cartridgeaccording to claim 1, which includes an end cap that seals an end of thecasing that is opposite from the tapered part.
 10. The rock breakingcartridge according to claim 9, wherein the cap is held on the casing bya retainer that is configured to release the cap from the casing upon apredetermined pressure being reached inside the internal cavity.
 11. Arock breaking cartridge comprising: a casing of deformable material,said casing having a front end and a rear end, wherein the casing hastwo tapered parts, at each of the opposing front end and rear end of thecasing, with narrow ends of said tapered parts being directed towardsthe front end and rear end, respectively, and with wider ends of saidtapered parts facing towards each other, said casing forming an internalcavity between the wider ends of the tapered parts; at least twodeformable seals, extending, at least in part, around the outsides ofthe tapered parts of the casing; two pistons disposed inside theinternal cavity, each of said pistons being dimensioned to but againstthe inside of one of the tapered parts of the casing and to seal againstthe inside of the casing; and a gas generating compound inside theinternal cavity between the two pistons.
 12. The rock breaking cartridgeaccording to claim 11, wherein the casing comprises two sub-casings,each of said sub-casings has a tapered part, and the sub-casings arejoined together in a sealing manner.
 13. The rock breaking cartridgeaccording to claim 2, wherein at least part of the piston has afrusto-conical shape.
 14. The rock breaking cartridge according to claim2, wherein the piston includes a rounded head that buts sealinglyagainst the inside of the tapered part of the casing, inside the seal.15. The rock breaking cartridge according to claim 2, which includesgrip formations that extend around the outside of the tapered part ofthe casing.